Unit D

Module 9 ~ Lesson 3

Energy for Muscle Contraction

The body's muscles require a continuous supply of energy in order to maintain their function. When the energy demands for muscle contraction exceed the reservoir of stored energy, the ability to control movements may be impaired to the point that normal voluntary coordination of even simple tasks like running are impossible.

Muscle contraction requires a continuous supply of energy in the form of ATP. There are three main sources of ATP.

  • creatine phosphate (sometimes referred to as the phosphagen system )

  • aerobic respiration of glucose

  • fermentation of glucose (also known as anaerobic respiration and/or as the lactic acid system )

Regardless of what source of ATP is used, when ATP is consumed during muscle contraction, the result is an ADP molecule and a phosphate molecule. These molecules are then cycled back into cellular respiration to create more ATP. The chart below summarizes each source of ATP.

During prolonged endurance exercise, such as running a marathon, a depletion of muscle sugar stores, a decrease in blood glucose, dehydration, or an increase in body temperature contribute to fatigue. During an intense muscular activity, lactic acid is formed through glycolysis and lactic acid fermentation.

The H+ ions from lactic acid decrease the pH of the muscle; this may inhibit metabolic processes and, thereby, decrease work output.


By Kebranch [Public domain], from Wikimedia Commons


Energy

Source

Aerobic or Anaerobic

Site of Reaction

Initial Reactant Required for Contraction

Final Products of Reaction

Relative Amounts of ATP Produced

Creatine Phosphate anaerobic doesn't require oxygen within the muscle myofilaments creatine phosphate creatine + ATP high, for a short period of time
Aerobic Cellular Respiration aerobic requires oxygen mitochondria of muscle cells glucose or fatty acids CO 2 + H 2 O + ATP high
Fermentation anaerobic, doesn't require oxygen the cytoplasm of muscle cells glucose or fatty acids lactate (lactic acid) + ATP low

 Read

Read " Energy for Muscle Contraction" on pages 339 to 342 of your textbook.